Optical networks and the like (e.g., Dense Wave Division Multiplexing (DWDM), Synchronous Optical Network (SONET), Synchronous Digital Hierarchy (SDH), Optical Transport Network (OTN), Ethernet, and the like) at various layers are deploying control plane systems and methods. Control planes provide an automatic allocation of network resources in an end-to-end manner. Exemplary control planes may include Automatically Switched Optical Network (ASON) as defined in ITU-T G.8080/Y.1304, Architecture for the automatically switched optical network (ASON) (02/2005), the contents of which are herein incorporated by reference; Generalized Multi-Protocol Label Switching (GMPLS) Architecture as defined in IETF Request for Comments (RFC): 3945 (10/2004) and the like, the contents of which are herein incorporated by reference; Optical Signaling and Routing Protocol (OSRP) from Ciena Corporation which is an optical signaling and routing protocol similar to Private Network-to-Network Interface (PNNI) and Multi-Protocol Label Switching (MPLS); or any other type control plane for controlling network elements at multiple layers, and establishing connections among nodes. Control planes are configured to establish end-to-end signaled connections such as Subnetwork Connections (SNCs) in ASON or OSRP and Label Switched Paths (LSPs) in GMPLS and MPLS. Note, as described herein, SNCs and LSPs can generally be referred to as services in the control plane. Also, note the aforementioned control planes are circuit-based control planes, e.g., operating at Layer 1 (Time Division Multiplexing (TDM)) and/or Layer 0 (wavelengths). Control planes use the available paths to route the services and program the underlying hardware accordingly.
Preemption is a process in a network where existing services are dropped or rerouted due to a lack of bandwidth for higher priority services. For example, preemption can occur when there is a fault, and higher priority services need to restore on a link, but the link has insufficient bandwidth. The preempted services can also attempt to restore. Thus, the preemption of one or more established SNCs or other services by another SNC in a control plane network causes increased instabilities as the preempted SNCs attempt to restore. Thus, it would be advantageous to limit the number of services affected by preemption. However, in a distributed control plane with a limited network view, such as GMPLS or ASON, network elements do not have visibility of all service paths in the network. While the originating (or source) network element can choose the lowest cost path for the service based on the knowledge of available bandwidth at a particular priority level on individual links, it does not have knowledge of the other services on those links; only the intermediate network elements know this information (intermediate network elements can also be referred to as transit network elements). Therefore, the originating network element cannot choose which services are preempted on individual links across the network.
Generally, the preemption process includes a SETUP message (in ASON, OSRP, etc.) or some other type of message, notification, etc. transmitted along the path of the service. The intermediate network elements choose one or more services on the link to preempt based on priority, rate, etc., but all based on the local knowledge of the services on the link. Service paths are not taken into account since this information is not available at the originating network element or locally on the intermediate network elements. Thus, if SNC A is preempted on the first link, SNC B may be preempted on the second link causing multiple SNCs to mesh restore. Whereas a more intelligent design maybe only SNC A released on both links. The preempting SETUP Message must be sent without the knowledge of how much instability the action will cause. The decision of which services to preempt must be made by the intermediate network elements. These intermediate network elements have no knowledge of service paths other than the two links in the preempting service's path connected to that network element. Similar to the originating network element, the decision of which services to preempt on these links may not be optimal due to this lack of network visibility.
Software Defined Networking (SDN) utilizes a centralized controller and may have a better view of the network allowing for more informed decisions about the preemption path and services to preempt. However, the level of knowledge may not be complete or may be inaccurate; especially in the case of a hybrid control plane which includes a distributed control plane overseen by a centralized controller where the network elements are given some level of control when restoring services. In the hybrid case, this occurs in two possible scenarios. First, if the network does not advertise services on individual lines within an aggregated link, the centralized controller cannot efficiently choose services to preempt on individual links. This is because it cannot know which lines within the link the preempting service will be assigned. This decision is made locally by the network elements. Second, if the network elements are allowed to perform route calculation during mesh restoration, the centralized controller may not immediately know where the services are routed in the network. This can occur if one or more originating network elements exhaust all protect routes provided by the centralized controller for one or more SNC's.
In circuit-based control planes, SDN, and hybrid control plane networks, it would be advantageous for optimized service preemption selection systems and methods that minimize the impact to other services during preemption.